package com.atguigu.KMP;

import java.util.Arrays;

/**
 * description:
 * Created by 才睡醒 on 2021-09-05
 */
public class KMPAlgorithm {
    public static void main(String[] args) {
        String str1 = "BBC ABCDAB ABCDABCDABDE";
        String str2 = "ABCDABD";

        int[] next = kmpNext("ABCDABD");
        int index = kmpSearch(str1, str2, next);
        System.out.println(index);
    }

    //写出kmp搜索算法
    public static int kmpSearch(String str1,String str2,int[] next){
        //遍历
        for (int i = 0,j=0; i < str1.length(); i++) {
            //kmp
            while (j > 0 && str1.charAt(i) != str2.charAt(j)){
                j = next[j-1];
            }

            if(str1.charAt(i) == str2.charAt(j)){
                j++;
            }
            if(j== str2.length()){
                return i - j + 1;
            }
        }
        return -1;
    }

    //获取到一个字符串（子串）的部分匹配值表
    public static int[] kmpNext(String dest) {
        //创建一个next数组 保存部分匹配值
        int[] next = new int[dest.length()];
        next[0] = 0;//如果字符串是长度为1，部分匹配值就是0；
        for (int i = 1, j = 0; i < dest.length(); i++) {
            //当dest.charAt(i) != dest.charAt(j) ,我们需要从next[j-1]获取新的j
            //直到发现有dest.charAt(i) == dest.charAt(j)成立才退出
            while (j > 0 && dest.charAt(i) != dest.charAt(j)) {
                j = next[j - 1];
            }
            //当dest.charAt(i) == dest.charAt(j)满足时，部分匹配值就是+1
            if (dest.charAt(i) == dest.charAt(j)) {
                j++;
            }
            next[i] = j;
        }
        return next;
    }
}
